The present invention relates to a method for controlling the speed of a vehicle, particularly under consideration of vehicles driving ahead.
From German Published Patent Application No. 42 42 700, it is known to mount a radar or infrared sensor on a vehicle to detect vehicles driving ahead. This radar sensor can be, for example, a module of a vehicle comfort and convenience system ACC (adaptive cruise control), in which information pertaining to the distance and the relative speed of the vehicle with respect to other vehicles and information on road conditions are continually processed.
The basic functions of the above described system relate to the control of the vehicle speed, either to a setpoint value, here the desired speed, or to the speed of a vehicle driving ahead, in the case that the latter is traveling at a slower speed than the desired speed and is within the sensing range of the radar sensor. As mentioned above, this sensor can be, for example, a component of a microwave radar or of an infrared lidar and, to that end, it measures the distance, the relative speed, and the angle of objects, particularly of vehicles driving ahead within the sensing range.
From German Patent No. 197 22 947, a method is known, where, in addition to measuring the quantities described above, the ACC system also includes the future travel-course progression of the vehicle, along with the ACC system, in the control in order to determine the future travel corridor. For this, the future travel-course range of at least one vehicle driving ahead is determined, and a lateral offset is then ascertained for all detected vehicles. Given steady-state curvature conditions of the roadway, i.e., in a linear portion or in the region of constant curvature of a curve, the future travel corridor is also able to be easily determined using the known method, with the aid of a well-adjusted yaw-rate or rotation-rate signal.
From the yaw rate of the ACC vehicle, the curvature of the roadway and, therefore, also the travel-course offset of a vehicle traveling ahead can be determined here, using generally known method steps. If this travel-course offset is smaller in terms of absolute value than a predefined width of the travel corridor, then one can infer that the vehicle traveling ahead is located in the travel corridor of the ACC vehicle. When working with changing conditions, particularly in the beginning curve region, however, one is normally no longer able to correctly determine the association with the travel corridor, so that it can happen that a vehicle driving ahead in the right, adjacent lane, near the beginning of a left curve, is incorrectly attributed to the travel corridor. This leads to faulty control reactions, the cause here being the mistaken curvature prediction, since the ascertained curvature is always specific to the current instant and, therefore, the reaction to a change in curvature is always too late.
A method for controlling the speed of a vehicle of the type mentioned at the outset, where, in the vehicle to be controlled, the yaw rate or rotation rate is measured, in particular to determine the curvature of the vehicle""s own travel trajectory, and where, using a proximity sensor or position sensor, at least one vehicle traveling ahead or at least some other object within a sensor""s sensing range is detected with regard to an offset from the travel course of the vehicle to be controlled, is advantageously further refined in accordance with the present invention.
As already mentioned at the outset, curvature k of the roadway may be calculated in a simple manner from the measured yaw rate of the ACC vehicle to be controlled using generally known method steps in that the yaw rate is divided by the speed, and, using that, the travel-course offset ye of a vehicle traveling ahead may also be determined. Specifically, travel-course offset yc may by determined by the following formula:
yc=yvxe2x88x92k*d2/2,
quantity yv being the measured lateral offset, without allowing for curvature k, and d being the distance between the vehicle to be controlled and the measured vehicle driving ahead.
If this travel-course offset yc is smaller in terms of absolute value than a predefined width ylane, then one may infer that the object or the vehicle is located in the travel corridor of the ACC vehicle, ylane corresponding approximately to one half of a lane width.
In accordance with the present invention, travel-course offset yc of a vehicle driving ahead, determined in preset measuring cycles, is delayed by a predefined time lag, and using the instantaneous curvature k of the travel trajectory of the vehicle to be controlled, a historical travel-course offset ychist is ascertained. In this context, the delay may advantageously be selected such that historical travel-course offset ychist is determined after approximately half of the distance between the vehicle to be controlled and the measured vehicle.
Therefore, alternatively to the generally known method of looking ahead using video-based lane detection or navigational systems, the method according to the present invention for controlling an ACC vehicle permits, in a simple manner, a relatively fast and simple-to-implement historical comparison between the position and travel trajectory of the vehicles. Instead of a costly, continuous transformation of the measured data, the present invention provides, in simplified fashion, for measured lateral offset yv to be delayed by about time span thist, commensurate with half of the time span between the vehicles.
From this so delayed value yvhist, as above, using active curvature k, the so-called historical travel-course offset ychist is now determined in accordance with the relation:
ychist=yvhistxe2x88x92k*dhist2/2
dhist being generated or estimated, likewise on the basis of a delay, as the historical distance between the vehicle to be controlled and the measured vehicle. For example, in accordance with the relation
dhist=dactivexe2x88x92vr*thist.
Thus, distance dhist takes into consideration the change in distance in response to speed differences. In illustrative terms, the mechanism functions as follows: the curvature determination is made approximately at the middle of the distance between the ACC vehicle and the measured object, although delayed by thist. Even when working with changing curvatures, the average curvature is a good estimation here and allows a quite precise determination of travel-course offset.
To avoid unwanted transient effects in those cases where the object had not yet been measured for the length of time span thist and, consequently, no historical lateral offsets exist, it is advantageous when a dynamically increasing delay time thist/dyn takes the place of time thist, the time span until maximum value thist is reached being supplemented by the dynamic component that increases with the duration of observation. Until this maximum value is reached, the quality of the thus calculable ychist is somewhat lower, but this value is always ready as a transitional value.
In addition, a filtering is advantageous to compensate for short-term curvature fluctuations caused by steering motion or signal noise. Since this filtering likewise delays the active signal by tfilter, the delay in the yv values must likewise last longer by approximately this value. The delay may be advantageously further modified, for example, by filter times of active curvature signal k. In this connection, the instantaneous value of curvature k of the travel trajectory of the vehicle to be controlled, at any one time, is delayed by a preset value for averaging purposes, this delay being considered as well in the determination of historical travel-course offset ychist.
Although the delay times are known, so that thist is generated from the sum of half of the time gap and the filter time, such modifications of time span thist may be useful in order to achieve a functional optimum by way of a total adjustment. This applies, in particular, when the quantities are not only filtered by a delay element, but are also averaged via low-pass-type filters. The latter is also used here for reducing measuring fluctuations. Delay element and averaging filter may be combined in simple fashion, for example, by using filters having a most constant possible group delay, e.g., Bessel filters or series-connected filters having a critical attenuation.
In summary, the method of the present invention enables historical travel-course offsets to be generated in simple fashion, in particular by combining averaging and delay, without necessitating a costly storing of lane data or transformation of such stored data. A rapid result is achieved, since one only has to wait for about half of the time gap up until the result.
To obtain a still further improved method for predicting the path of the vehicle to be controlled, it is also possible for a number of further detection devices for determining the travel-course offsets of objects traveling ahead to be present in the vehicle to be controlled. All results of these detection devices may then be analyzed and weighted. The analysis and weighting may preferably be carried out using a video camera, a preferably satellite-supported navigational system, a set-up for analyzing fixed destinations, or a set-up for determining a collective yaw or rotation rate of the objects driving ahead.